The moisture in those early plaster molds was expelled by baking them in an oven for three or four hours. A later method for drying was practiced by suspending the mold directly over the metal-pots or to float them on the surface of the molten metal. By this means the drying could be accomplished in a half-hour or so.
In the process of casting, several of these plaster molds were placed side by side face downward in a special casting-pan. The pan was one and three-quarters or two inches deep, and a lid on the pan screwed down on the back of the molds. By means of a crane the casting pan with its molds was then lowered into the pot of molten metal which ran into the pan at the corners and sides. The mold was allowed to remain ten minutes or so in the metal-pot, or until the face of the inverted mold was entirely filled with the metal.
A later method of casting from a plaster mold was to place it in a frame with a smooth, flat plate opposite the face of the mold and to enclose the open space at one end and on the two sides. The casting space thus formed was then turned with the open end up and metal was poured in with a ladle, in a manner similar to the method still employed for casting job-work stereotypes. The distance between the flat plate and the mold was adjusted to make a stereotype plate of the required thickness.
After the removal and cooling of the casting pan, the plates were freed from the plaster and the surplus metal cut off. Only one cast could be made, as the mold was usually destroyed in removing the cast. The stereotype was then sent to the finishing department, where the face was cleaned and examined for defective letters, then trimmed on the sides and planed off uniformly on the back to the desired thickness, in the same manner as a stereotype is treated today. A defective letter could be mortised out of the plate and a good type inserted in its place. In cases where a whole line or other part was imperfect, another mold was made of as much of the form as was necessary and the new cast inserted and soldered to the plate.
There were many and varied experiments made in the earlier development of this idea of producing a duplicate printing form in a single piece. That such a process was highly desirable was universally recognized, and the conviction that some practicable and economical method was feasible was a continual incentive which gradually led to better results.
STEREOTYPING
IN AMERICA
Although credit is given to John Watts, an Englishman then working in America, for making the first stereotype plates here, the real introduction of the process into the United States was by David Bruce.